Blood pressure follower



Aug. 4, 1964 J. H. GREEN 3,143,111

BLOOD PRESSURE FOLLOWER Filed Sept. 23, 1960 5 Shets-Sheet 1 PRESSURE GAGE r 2? I5 I ll R l 3| PRESSURE PUMP Mom 4" RESERVOIR PRESSURE f Aug. 4, 1964 J. H. GREEN 3,143,111

BLOOD PRESSURE FOLLOWER Filed Sept. 23, I960 5 Sheets-Sheet 2 5 Sheets-Sheet 3 J. H. GREEN BLOOD PRESSURE FOLLOWER Aug. 4, 1964 Filed Sept. 23, 1960 I. m m E53 F u 2353 z a 2 m 3%,, mm a w (A 2 21 BK no N.

on m m umammuza Aug, 4, 1964 J. H. GREEN BLOOD PRESSURE FOLLOWER 5 Sheets-Sheet 4 Filed Sept. 23 1960 Aug. 4, 1964 I H, GREEN 3,143,111

BLOOD PRESSURE FOLLOWER Filed Sept. 23, 1960 5 Sheets-Sheet 5 l47/ 5 I I62 I74 United States Patent "ice 3,143,111 BLOOD PRESSURE FOLLOWER John H. Green, Pinner, England, assignor to Winston Electronics Limited, Shepperton, England, a British company Filed Sept. 23, 11960, Ser. No. 58,115 3 Claims. (Cl. 128-213) This invention relates to improvements in devices for measuring blood pressure and particularly to devices which give a continuous reading and recording of such blood pressure together with means for controlling the blood pressure of the patient within allowable limits.

The usual method of measuring blood pressure consists of using an inflatable cuff strapped to the limb of the patient and connected to a sphygmomanometer, such as a column of mercury. By means of a stethoscope, the operator estimates, from the sounds he hears, the instant the cuff pressure passes through the systolic and diastolic blood pressure values. These readings are determined by inflating the cuff to a pressure beyond the systolic pressure and allowing this pressure to decay. The pressure is visually read from the mercury column when the systolic and diastolic sounds are detected through the stethoscope. Such a method is cumbersome and requires great skill by the person reading the blood pressure. Automatic devices have been developed for providing direct readings of blood pressure on a meter, but these automatic systems have serious limitations. The cuffs which are conventionally used in the systems now in use cannot be left on the patient for a long period since they seriously hinder the flow of blood in the limb on which they are placed. Therefore, the readings obtained, even in the so-called automatic systems, merely provide a series of individual blood pressure readmgs.

Accordingly, it is an object of this invention to provide a device which will provide a continuous reading and recording of blood pressure.

Another object of this invention is to provide a continuous blood pressure follower which may be used on a patient for a very long period of time without causing discomfort or injury to the patient.

Yet another object of this invention is to provide continuous readings of blood pressure on a dial as well as on a sphygmomanometer and at the same time give a continuous recording of the blood pressure.

A further object of this invention is to provide a blood pressure follower which may be used with conscious or unconscious patients in all branches of medicine where blood pressure readings are required.

A still further object of this invention is to provide a blood pressure follower which controls the administration of hypoor hypertensive drugs to a patient if the pressure falls below or exceeds predetermined limits.

Further objects and advantages of this invention will become apparent to those skilled in the art by referring to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified diagrammatic showing of a blood pressure follower system as contemplated by the present invention;

FIG. 2 is a sectional view of a digital cufl? or sleeve means which may be used in conjunction with the present equipment;

FIG. 3 is a perspective view of an electrical transducer which may be used in the system for detecting the pulse pressures;

FIG. 4 is a showing of the method of applying the cuff of FIG. 2 and the transducer of FIG. 3 to a digit of the patient;

FIGS. 50v and 5b are schematic circuit diagrams of the 3,143,]. l l Patented Aug. 4., 1964 entire system including the blood pressure follower, recorder and drug control panel; and

FIG. 6 is a perspective view of a cabinet containing the equipment of FIGS. 5a and 5b and showing a preferred arrangement of the dial and indicator devices.

In the blood pressure follower of the present invention, the arterial pulsation from the digital artery of a finger or toe is picked up by a piezoelectric crystal placed over this artery. Each of these pulsations is employed to open a normally closed air valve which inflates a cuff or sleeve means from a small pump in the apparatus. The cuff occludes the artery proximally to the point of application of the crystal, and when this occlusion is complete the air valve is no longer actuated and a leak in the pressure system allows the cuff to deflate until pulsations reappear. Each of the pulsations causes the valve to open temporarily and allow further air to enter the cuff. The apparatus thus maintains the pressure within the cuff at substantially the same level as that of the digital artery.

The cuff or sleeve means of the present invention has been designed substantially to enclose the finger and to raise the pressure of the finger tissues to a level which varies above and below the arterial pressure. In this Way, the cuff acts as a G-suit on the finger and allows the normal exchange of tissue fluid, nutrition and metabolites to continue with the blood flow which occurs when the cuff pressure is below that of the digital artery pressure. This, coupled with the low metabolism of the finger, permits the cuff to be kept in position for periods of four hours or more without cyanosis or oedema developing. The cuff is quite comfortable to the patient and there is no ischaemic pain during use. Referring now to FIG. 1, an electric motor 11 drives an air pump 15 through any suitable mechanical linkage represented at 13. Pump 15 provides air under pressure to a solenoid control valve 19 through conduit 17. When the valve 11 is open, air passes through conduit 21, through a manually adjustable inflation valve 23 and through conduit 25 into a pressure reservoir 27. A manually controllable deflation valve 29 is placed between the inflation valve 23 and the reservoir 27. The inflation valve 23 and the deflation valve 29 are adjusted relative to each other according to the desired operation of the system. It has been found that an adjustment allowing the inflation valve 19 to pass one and one-half times the amount of air that is allowed to pass through the deflation valve29 results in satisfactory operation of the system. Since the solenoid control valve 19 is continually opening and closing due to the arterial pulsations within the digit, the pressure reservoir 27 is provided to absorb minor pressure variations and deliver a smooth flow of air at a slowly varying pressure to conduit 31.

The pressure in conduit 31 inflates the cuff or sleeve means 33 to a value where it is slowly varying above and below the systolic pressure as detected by the transducer 37 which is strapped to the finger within the cuff 33. A pressure gauge 35 gives a direct reading of the pressure within conduit 31 and, therefore, a direct reading of the systolic pressure of the patient. Arterial pulsations cause a signal to be developed by transducer 37 and these signals, which are amplified by amplifier 39, open the solenoid valve 19 which remains closed unless energized.

The associated pressure operated equipment 40 may also be connected to conduit 31 in order that the pressure within the cufl may be used to control this equipment. The system will operate properly with any device which is designed so as to provide a pressure on the digit which slowly varies about the systolic pressure within the artery. A highly successful, inexpensive device for applying such a pressure is shown in FIG. 2 which is a sectional view taken through the length of the cylindrical cufl 33. Cufl 33 comprises an outer cylindrical sleeve 41 of a material which is flexible but non-stretchable. An inner liner sleeve 43 of generally cylindrical shape is secured within the outer sleeve 41 at the ends 45. The liner 43 may be made of the same material as the sleeve 41 and is expandable within the sleeve 41 and thus, constricts the diameter of the opening through the cuff 33 when inflated. The sleeve 4-3 may be secured to cylinder 41 by heat sealing or with a suitable adhesive depending upon the material used. An opening is provided in the body of the sleeve 41 in which is secured a hose 49 for supplying the air for pressurizing the cuif. The cuff may be formed of any suitable plastic material such as polyvinyl chloride.

Although the system will operate with any of the wellknown electrical transducers, the particular transducer of FIG. 3 has proven to be advantageous in that it avoids the possibility of signals being produced due to the air pressure in the cult rather than the pulsating pressure of the artery. The transducer 37 of FIG. 3 comprises a base plate 53 which may be of any rigid material, and, in order to provide a support for the crystal 59, a crosspiece 55 of dielectric material is secured between one end of the plate 53 and one end of the crystal 59. A small block of dielectric material 57 is secured at one corner on the opposite end of plate 53 between the plate and the crystal. The pressure exerted at or near the unsupported corner 61 of the crystal 59 will cause the crystal plate to twist and thus induce a signal in the leads 63. If the block 57 is not used, the signal will be induced in the crystal by a pressure exerted on the free end thereof. It has been found that such an operation often results in an unwanted signal being induced by the air pressure of the cuff, and, if the pressure of the cult should become great enough, then the crystal would come into contact with plate 53 and destroy the operation of the device 37 entirely. The transducer shown in FIG. 3 substantially eliminates such a possibility.

Transducer 37 is wrapped in a protective coating and is secured to the digit of the patient 65 as indicated in FIG. 4. A mark 67 is preferably placed on the wrapping adjacent the base plate 53 to indicate the free corner 61 of the crystal 59. This mark is placed over the digital artery 69 and the unit is secured to the finger by means such as tape 70, here shown as transparent tape for purposes of clarity. Leads 63 extend outwardly from the finger to a connector 71 which provides a means for connecting the signal output of the crystal to the control circuits of the system. The cult 33 is slipped over the digit so as to enclose the transducer 37 with the leads 63 extending beyond the cult The cult is then inflated and the automatic process is put into operation.

FIG. 5a is a schematic showing of the controls for the pressure follower. The electric motor 11 is supplied from a standard single phase three-wire source V when the main switch S (FIG. 5b) is closed. The path of the air under pressure from the pump 15 through the conduits, valves and reservoir to the cufi is as explained in the discussion in connection with FIG. 1.

The power source for the amplifying and control circuit is derived from the power supply V through transformer T Two full-wave rectifying tubes V and V are connected across a secondary of transformer T and provide equal voltage outputs having opposite polarities. The output rectifier V provides the plate supply voltage for the various components and the power for operating the solenoid valve. The output of rectifier V provides the negative voltage bias for the various cathode elements used in the tubes The leads 63 and 64 from the transducer 37 are connected to the input terminals 115 and 116 of the amplifying and control circuit. Since leads 63 and 64 are necessarily relatively long, the circuit connections to tube V are employed in order to eliminate any induced signals which might appear in the leads. The signal from terminal 115 passes through resistor R to the control grid 121 of the dual triode tube V The signal from terminal 116 passes through resistor R to the other control grid 122 of tube V Equal resistors R and Po; connect terminals 116 and to ground.

In accordance with standard operation, the signals appearing in leads 63 and 64 are of opposite phase as is usual with the output of a crystal transducer and the signals from the transducer 37 appear at the control grids 121 and 122 of the tube V out of phase. Because of the differential amplifier arrangement of tube V this signal is amplified. However, any signals which are induced in leads 63 and as by means other than the transducer 37, such as hum and lead movements, appear at the control grids 12 1 and 122 in phase and are cancelled by the differential amplifier. Thus, any spurious signals induced in the leads are cancelled. Capacitors C and C remove any high frequency signals which may be present due to the operation of hi h frequency equipment in the vicinity. The anodes of V are connected through capacitors C and C to opposite grids of dual triode tube V The output of tube V is passed through a double-T network 125 to the grid 127 of tube V Anode 129 of tube V is connected through capacitor C to the control grid 131 of tube V A manual gain control 134 is provided for adjusting a variable resistor VR through a mechanical linkage for controlling the gain of the amplified signal which appears on grid 131. The protective resistor connected in parallel with resistor VR is of a comparatively large magnitude and is included to partially reduce the sensitivity of adjustments of VR A switch S is provided in the circuit to control the switch arms 8 S and S which are ganged, three position switches. Switch S controls the position of valve 19 and, thus, the inflation and deflation of the cuff 33. The three positions of the switch are inflation deflation and automatic (auto). When the switch is in the inflation position as shown in FIG. 5a, the plate supply for anode 133 is through lead 135, pulse indicator milliammeter 137, through switch S resistor R and resistor R to rectifier V Since the valve 19 remains closed unless the solenoid 139 is energized, current must be supplied to the solenoid when the switch is in the inflate position. This current is supplied from rectifier V through resistor R switch S to solenoid 139 and switch S to ground. Thus, when switch S is in the inflate position, the signal output or lack of signal output from the double triode V has no effect on the operation of the valve since the solenoid is continually energized.

When switch S is moved to the deflate position the plate supply to the anode 133 remains the same. However, switch S opens the circuit to the solenoid and the deenergized valve 19 closes allowing the cuff to deflate through deflation valve 29.

When the switch S is moved into the automatic position (auto) the plate supply through resistor R is removed. However, the value of resistor 37 is matched to the value of the internal resistance of the solenoid 139. Therefore, when the switch is in the auto position the plate supply is through lead 135, milliamrneter 137, switch S switch S through solenoid 139, switch S and resistor R to rectifier V Accordingly, every pulse that passes through the pulse indicator 137 will energize the solenoid and open the valve 19 allowing air under pressure to pass therethrough. It is also to be noted that the operation previously described acts as an integrating circuit in that the valve 19 will remain open for the approximate period of time equal to the width of the pulse passing through the pulse indicator. As the pressure increases and the pulsations become Weaker, a shorter pulse will be generated and the valve 19 will open for a shorter period of time. This prevents excessive hunting about the systolic pressure when the system is in operation.

The normal procedure followed when the digit and transducer are in place within the cuff is to switch S to the inflate position which causes valve 19 to remain open.

After the pressure within the end, as indicated by pressure gauge 35, reaches a nominal amount such as 40 mm. of Hg, switch S is placed in the automatic position. Transducer 37 detects the arterial pulsations of the digit causing valve 19 to open with each pulsation, allowing air to pass therethrough. The pulses from the transducer 37 will continue on a gradually diminishing scale until the systolic pressure is reached in the cuff, at which time no signal will appear to energize solenoid 135 and valve 19 remains closed. The pressure system will then gradually begin to deflate through valve 29. When the pressure in the cult is reduced to slightly below the systolic pressure arterial pulsations will reappear and inflation will again occur. Accordingly, the pressure gauge 35 will vary slightly in a rhythmic manner about the systolic pressure.

Glow tubes V V V and V are provided in order to insure a stable voltage supply from the rectifiers and capacitors C 12, C and C are provided for smoothing purposes.

Additional secondary windings are provided in transformer T to supply the necessary current for the various cathode heaters as indicated at a, b and c. An indicator lamp, such as a red light 143, is connected across one of the secondaries to give a positive indication that power is being supplied to the transformer T FIG. 5b shows the recorder and drug control panel which may be connected to the pressure system by means of a standard connector 138. Recorder 139 is provided with a small torque motor 142 which receives its power supply from the main power source V Motor 142 drives a reel to move a heat sensitive paper at a constant speed past the recorder and marker pens. This paper drive mechanism is of a standard type and is not shown in FIG. 5b for purposes of clarity. Air pressure equal to that of the cult passes through valve 109 and actuates a bellows 140 which moves a recorder pen 144 through a mechanical linkage 145. The recorder pen 144 is of the hot wire type and receives current from the secondary transformer T through resistance R Thus, a continuous recording on the heat sensitive paper of the systolic blood pressure of the patient is available. There is also provided a marker pen 146 which is also of the hot wire type. Current is supplied to pen 146 only when switch S is held in a depressed condition. This allows the intermittent marking of the heat sensitive paper for purposes of indicating the commencement and ending of certain test periods, the injection of drugs, etc. Indicating light 143 is provided to give a visual showing that switch S is closed and the recorder is in operation.

Two adjustable pressure switch actuators 146 and 148 are also connected to conduit 32 through connector 138 and valve 111. These adjustable pressure switch actuators control administration of hype and hypertensive drugs to the patient. Actuators 146 and 148 are of the well-known type which are manually adjustable through linkages connected to control knobs 147 and 149 which adjust the tension on the diaphragm within the switch. Pressure switch actuator 146 is adjusted to the allowable lower limit to which the blood pressure may fall while actuator 148 is adjusted to the allowable maximum limit to which the blood pressure may rise. Power is supplied to the drug control circuit from the voltage source V through the transformer T when switch S is closed. Rectifying bridge MR is connected across the secondary of transformer T with the output of the rectifier passing to the switch arm 151 of pressure switch 146. The switch arms 151 and 154 are shown in their normal position which exists when the pressure in the conduit is between the set upper and lower limits of actuators 146 and 148. Under this condition, current passes from the rectifier through switch arm 151, through an indicating lamp 159, such as a green light, and through switch 154 to ground. Outlets 161 and 162 are provided in parallel with light 159 and may be used for any other indicating purpose, such as an audible alarm which would sound should the current through the switches be cut 011. Remote visual indicating lamps could also be connected to one of these outlets.

Should the pressure in the conduit fall below the set allowable lower limit, pressure switch actuator 146 will move switch arm 151 to terminal 164, thus opening the circuit through indicator light 159 and closing the circuit through indicator light 166, such as red light, and outlet 167. This energizes the solenoid 169 which is connected to outlet 167 and opens a valve in a drug container 170 to allow the proper drug to be delivered to the patient. Normally, the drug container 170 would be such that it provides drip gravity delivery to the patient through a tube and a needle in the patients arm. Should the pressure exceed the allowable limits, pressure actuator switch 148 will move arm 154 into contact with termainl 172. This will also open the circuit through light 159 and cause a similar operation of solenoid 175 which will deliver the opposite type of drug to the patient. Thus it can be seen that fully automatic control of the blood pressure of the patient is achieved by the system of this invention.

FIG. 6 shows the cabinet in which the equipment is housed and the preferred arrangement of the associated dials, indicators and control knobs. The cabinet is formed in two main compartments, the upper compartment 178 housing the pressure control equipment illustrated in FIG. 5a and the lower compartment 179 housing the recorder and drug control equipment shown in FIG. 5b. The upper compartment 178 slips over the lower compartment at the flange 180 and is removable therefrom bymerely disconnecting the mechanical release, the electrical leads from the main power source and the pressure conduit from the main pressure line at connector 138 of FIG. 5b. Thus, the air pressure control and indicator equipment is removable from the main cabinet so as to be usable in a portable manner.

Dials 24 and 30 provide the manual control of inflation valve 23 and deflation valve 29, respectively. As explained hereinabove, this setting is made prior to placing the equipment in operation. The manual switch S provides the control for automatic operation and manual inflation or deflation. Knob 134 controls the gain of the output to pulse indicator 137 which indicates the presence of a pulse. Pressure may be read visually on either the pressure gauge 35 or the mercury sphygmomanometer 106 which is detachable from the equipment if desired.

The lower compartment 179 of the cabinet has a sliding drawer 132 which houses the recording equipment shown in FIG. 5b. The manual controls for the drug control equipment are provided on the face of the lower compartment. Dials 147 and 149 provide the adjustment of pressure switches 146 and 148, respectively. The red indicator lights 166 and 173 indicate, when illuminated, that the blood pressure is either below or above the set limits, while the jacks 161, 162 are the outlets for the alarm circuits. The connections to the solenoids 169 and are provided through the jacks 167 and 174. Wheels 184 are provided in order to facilitate movement of the cabinet to the desired position.

The blood pressure follower of the present invention has many uses throughout the whole field of medical practice. The use of this instrument in an operating room gives continuous blood pressure readings on the dial, the mercury column and the chart recorder as well as providing complete control of blood pressure through the automatic application of drugs. During the recovery phase of an operation the continuous information as to blood pressure changes is available even though the patient may be under the influence of anesthetic and drugs The specification and drawings are illustrative only of one preferred embodiment of the present invention and are not to be considered as limiting the invention in any manner. Many changes could be made in individual elements ior in the circuitry used for controlling these elements, and such changes would be obvious to any person skilled in the art in the light of this disclosure. Such modifications are considered to be within the scope of the present invention as defined in the appended claims.

The present application is a continuation-in-part of my co-pending application Serial No. 763,957, filed Septem ber 29, 1958, and now abandoned.

I claim:

1. A system for the continuous control of blood pressure in a digit comprising a cuff for application to a portion of said digit and including flexible inflatable means, pneumatic pressure means connected to said inflatable means, a pressure transducer within said cuff adjacent to said digit for producing a signal in response to each arterial pulsation in said digit, a normally closed air valve between said pneumatic pressure means and said inflatable means, means controlled by said transducer for temporarily opening said valve in response to each of said signals produced by said transducer, means connected to said inflatable means for indicating the pressure therein, at least one drug container, means for controlling the flow of drugs from said container, an adjustable pressure actuator connected to said means for controlling the flow of said drugs, and means connecting said pressure actuator to said inflatable means whereby said actuator is operated when the pressure in said inflatable means reaches a predetermined limit.

2. The apparatus of claim 1 further comprising indicating alarm means connected to and operated by said pressure actuator.

3. A system for continuously measuring the blood pressure in a digit comprising an electric motor driven fluid pressure pump, an inflatable cuff for substantially sufrounding said digit and connected to said pump by a conduit, a solenoid, a valve in said conduit between said pump and said cufi, means connecting said solenoid to said valve, said valve being open when. said solenoid is energized, manually adjustable inflation and deflation valves in said conduit between said cuff and said solenoid operated valve, a pressure gauge connected to said cuff for indicating the pressure therein, a transducer'adjacent to said digit within said cuff for producing a signal in response to each arterial pulsation within said digit, means connected to said transducer for amplifying said signals, a manually operable three position switch for controlling said soleniod, said solenoid being continually energized when said switch is in its first position and deenergized when said switch is in its second position, the output of said amplifier being connected to said solenoid when said switch is in its third position so that each arterial pulsation in said digit energizes said solenoid, a recording means having a movable pen, a bellows for actuating said pen, conduit means connecting said bellows to said cuff whereby the movement of said bellows is controlled by the pressure within said cuff, first and second drug containers each having solenoid actuated fluid valves therein, first and second normally open switches for energizing said solenoid actuated fluid valves respectively, a first and second adjustable pressure operated means for closing said first and second switches respectively, and conduit means connecting said first and second pressure operating means to said cuff whereby said pressure operating means are controlled by the pressure within said cufi.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,033 Garceau Oct. 8, 1946 2,452,799 Speaker Nov. 2, 1948 2,690,173 Bickford Sept. 28, 1954 2,826,191 Burns Mar. 11, 1958 2,848,992 Pigeon Aug. 26, 1958 2,851,030 Boucke Sept. 9, 1958 

1. A SYSTEM FOR THE CONTINUOUS CONTROL OF BLOOD PRESSURE IN A DIGIT COMPRISING A CUFF FOR APPLICATION TO A PORTION OF SAID DIGIT AND INCLUDING FLEXIBLE INFLATABLE MEANS, PNEUMATIC PRESSURE MEANS CONNECTED TO SAID INFLATABLE MEANS, A PRESSURE TRANSDUCER WITHIN SAID CUFF ADJACENT TO SAID DIGIT FOR PRODUCING A SIGNAL IN RESPONSE TO EACH ARTERIAL PULSATION IN SAID DIGIT, A NORMALLY CLOSED AIR VALVE BETWEEN SAID PNEUMATIC PRESSURE MEANS AND SAID INFLATABLE MEANS, MEANS CONTROLLED BY SAID TRANSDUCER FOR TEMPORARILY OPENING SAID VALVE IN RESPONSE TO EACH OF SAID SIGNALS PRODUCED BY SAID TRANSDUCER, MEANS CONNECTED TO SAID INFLATABLE MEANS FOR INDICATING THE PRESSURE THEREIN, AT LEAST ONE DRUG CONTAINER, MEANS FOR CONTROLLING THE FLOW OF DRUGS FROM SAID CONTAINER, AN ADJUSTABLE PRESSURE ACTUATOR CONNECTED TO SAID MEANS FOR CONTROLLING THE FLOW OF SAID DRUGS, AND MEANS CONNECTING SAID PRESSURE ACTUA- 